The human interferon alfas are a family of proteins comprising at least 24 subspecies, Zoon K. C, Interferon 9:1 (1987), Gresser I., ed. Academic Press, New York. They were originally described as agents capable of inducing an antiviral state in cells but are known as pleitropic lymphokines affecting many functions of the immune system, Opdenakker, et al., Experimentia 45:513 (1989). Apart from their in vitro biological activities the human interferon alfas are currently used for several indications, e.g., hairy cell leukemia, Kaposi's Sarcoma, venereal warts, hepatitis B and hepatitis C.
Interferon alfa-2b is a purified sterile, lyophilized recombinant interferon formulation. The demand for highly purified and crystalline forms of interferon alfa, especially the recombinant type alfa-2b is of foremost importance for structure elucidation as well as for formulation of various dosage forms including the development of sustained release formulations.
Two forms of crystalline human interferon alfa have been reported, namely from Miller et al., Science, 215:689 (1982); Kung et at., U.S. Pat. No. 4,672,108; Weissmann, The Cloning of Interferon and other Mistakes, In: Interferon 1981, Ian Gresser, ed., Academic Press, New York, 101-134; Weissmann, Phil. Trans. R. Soc. Lond. B299:7 (1982); Nagabhushan, et al., `Characterization of genetically Engineered alpha-2 Interferon`, In: Interferon: Research Clinical Application and Regulatory Consideration, Zoon et at., Elesvier, N.Y. 79 (1982). These publications describe methods for crystallizing interferon alfa-2 from polyethylene glycol at low temperature or from a phosphate buffer solution by adjusting the pH or temperature. The Miller et al. article also mentions crystalline alfa-2 in a "prismatic form". Conditions for producing monoclinic prismatic crystals of interferon alfa-2b from solutions of ammonium sulfate in vapor diffusion hanging drop experiments at 22.degree. C. are disclosed in International Patent Application No. PCT/US 91/03660.
IFN-.alpha. is generally administered either by subcutaneous or intravenous injection usually in hospital or clinical settings. IFN-.alpha. has a serum half-live of 2-6 hours when injected subcutaneously or minutes when injected intravenously, and characteristically shows a "burst" or a "pulse" (rapid blood serum clearance rate) profile when blood levels are measured over time. Thus frequent administration of doses of the protein must be made to maintain a therapeutically effective blood serum concentration of the drug. There are clinical situations when it may be therapeutically more advantageous to develop an IFN-.alpha. formulation in which the protein is continuously released into the blood stream so that the serum concentration of the protein reaches a plateau and remains at that level for sustained period of time. This is known as a sustained release formulation.
To date none of the known crystalline IFN-.alpha. have shown properties desirable for a sustained drug delivery system, in particular, limited solubility at 37.degree. C. and stability in a `Generally Recognized as Safe` (GRAS) category formulation suitable for injection. There are a number of potential advantages of a sustained release therapeutic. Primarily, sustained release drugs can be administered at lower effective doses which improves their safety while maintaining or improving their efficacy. New therapeutic indications can be explored because prolonged bioavailability offers the opportunity for increased biodistribution to enhance tissue and organ penetration.
There is thus a need for a sustained-release formulations of IFN-.alpha.. SUMMARY OF THE INVENTION
The present invention provides for crystalline zinc-interferon alfa-2 (IFN .alpha.-2) having a monoclinic morphology. The present invention further provides for crystalline cobalt-IFN .alpha.-2, crystalline calcium-IFN .alpha.-2, and crystalline IFN .alpha.-2 having a serum half-life of at least about 12 hours when injected subcutaneously into a primate.
The present invention further provides for a method for producing a crystalline IFN .alpha.-2 comprising forming a soluble metal-IFN .alpha.-2 complex and equilibrating the soluble metal-IFN .alpha.-2 complex in solution with an acetate salt of the metal under conditions that will cause the metal-IFN .alpha.-2 solution to become supersaturated and form crystalline metal-IFN .alpha.-2.
The present invention includes crystalline metal-alfa interferon having monoclinic, plate and needle morphologies.